Diurnal and Spatial Variability of Tornadogenesis and Forecasting in Tropical Cyclones

Landfalling tropical cyclones generate many hazards like storm surge, wind damage, heavy rainfall totals, potential for flash flooding, and tornadoes. Forecasting these multiple events is problematic as forecasters are unable to focus on just one type of hazard. Given this and less clarity in the environmental parameters and radar attributes of the cells that produce them, there is often a high false alarm rate for tornado warnings within tropical cyclones. To improve the ability to forecast tornadoes in these unique conditions, understanding the relative location and timing of tornadic events is key. Additionally, identifying differences in the near-storm environmental conditions associated with tornadic and nontornadic cells and their spatial and temporal variability is expected to yield more accurate forecasts.

Using storm reports and radar data, cells were identified as tornadic or non-tornadic, and tornadoes were identified as warned or non-warned for all landfalling US tropical cyclones in the 2018 season. Soundings of the near-storm environments for each cell were gathered from Rapid Refresh (RAP) numerical model analyses, from which relevant convective parameters were calculated and compared. This analysis shows there is a clear diurnal cycle in tropical cyclone tornadoes, as there is a peak in tornado frequency in the late afternoon. Results will be presented investigating how changes in the near-storm environment contribute to the diurnal cycle in tornadoes. These same parameters were examined spatially and showed patterns of change relative to time after landfall and distance from the tropical cyclone center. Finally, variability in forecasting skill scores (both spatially and temporally) relative to the diurnal cycle and tropical cyclone position are examined.